1. Technical Field
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device including an electric fuse.
2. Related Art
There has been a technique by which a fuse is provided in a semiconductor device, and the value of the resistance used in the semiconductor device is adjusted, or a defective element is detached and is replaced with an appropriate element by cutting off the fuse.
To cut off a fuse, a laser beam is emitted onto part of the fuse, or current is applied to the fuse.
Japanese Patent Application Laid-Open (JP-A) Nos. 2005-39220, 2005-57186, and 2006-253237 disclose electric fuses that are cut off when the material forming each fuse moves due to electromigration.
JP-A No. 2005-39220 discloses a fuse that can be cut off by a small amount of current. In JP-A No. 2005-39220, the conductive material forming the fuse is bent several times. JP-A No. 2005-57186 discloses a structure in which the lower portion and the upper portion of the fusing area are covered with a plate, and a side of the fusing area is covered with a via.
JP-A No. 2006-253237 discloses a fuse device that includes a first wiring, a second wiring formed above the first wiring via an insulating film, and a first via that is formed in the insulating film so as to connect the first wiring and the second wiring. The first via is mainly made of a material that is more likely to cause electromigration than the main components of the first wiring and the second wiring. JP-A No. 2006-253237 also discloses a structure in which a heater wiring that heats the via is placed in the vicinity of the via. With this arrangement, the temperature in the area surrounding the via is increased at the time of via cut-off, so that the via can be efficiently cut off.
The present inventors have recognized as follows. In a case where a fuse is cut off when the material forming the fuse moves due to electromigration as disclosed in JP-A Nos. 2005-39220, 2005-57186, and 2006-253237, the material moves to cause a reconnection at the cut-off portion, if a heat treatment is performed on the semiconductor device after the fuse cut-off, or if the semiconductor device is exposed to the heat that is generated in practical use. If such a reconnection is caused, a correct result cannot be obtained when a check is made to determine whether the electric fuse that has been cut off is in a cut-off state. The probability of such a reconnection is not very high, and it is considered that no problems are caused in regular operations. However, in a case where the semiconductor device is expected to have very high reliability or is used under severe conditions, it is necessary to improve the retention properties so as to maintain the electric fuse in a desirable cut-off state.
To solve the above problem, JP-A No. 2007-305693 discloses a novel method for cutting off an electric fuse so-called a crack assist type process. According to this process, the structure of the electric fuse and the voltage application to the electric fuse are controlled so as to forcibly cause the conductive material of the electric fuse to flow out at a part of the electric fuse and to flow into the insulating film existing in the vicinity of the conductive material. By doing so, the balance between the material flowing-out and supply is upset, and a large cut-off portion is formed in another area. In this manner, the probability of a reconnection of a cut-off electric fuse can be made much lower, and a desirable cut-off state can be maintained.
In an electric fuse that is cut off in the above manner, however, the flowing-out of the conductive material becomes large. Therefore, it is necessary to control the location of the flowing-out of the conductive material and the movement of the flowing-out portion of the conductive material.